The invention relates to an eccentric gear wheel transmission for stepping up the rotary motion of adjusting motors. For reducing the rotary speed of adjusting motors, with an armature rotary speed of about 7000 rpm, worm gears are used as a rule. The worm gears used, which are driven by electric motors, are distinguished in that they have self-locking from the power takeoff side. Because of the requisite high gear ratio to attain adequate torques, for instance for driving window controls or a sliding roof in a motor vehicle, the external dimensions of an adjusting motor, comprising a motor and gears disposed side by side, are considerable. For this reason, eccentric gear wheel transmissions are used, which with very compact dimensions have self-locking and a simple design. Compared with the known worm gears, the eccentric gear wheel transmission is comparatively insensitive to tolerances, since all the rotating parts are supported on the same shaft.
An essential component of the eccentric gear wheel transmission is an eccentric wheel, which by its construction is capably of executing two different motions. One is rolling along a set of external teeth of a slaving means, which leads to a circular motion about a pivot point that is eccentric to the axis of the eccentric wheel, and the other is a rotation about itself. The rotation about itself is undesired, and in the known versions, it is prevented by guide elements on the eccentric wheel, which protrude into suitable recesses of a housing part connected solidly to the housing.
A disadvantage of this type of guidance is the major wear, caused by severe mechanical stress on the components involved in guiding the eccentric wheel, and the attendant short life of the eccentric gear wheel transmission, as well as the irritating noise produced by oscillating components.
The eccentric gear wheel transmission according to the invention having the characteristics of the main claim has the advantage that the guidance of the eccentric wheel is improved substantially. By means of the guide pinion cooperating with the eccentric wheel and assuring the circular motion of the eccentric wheel and preventing undesired rotation of the eccentric wheel, the mechanical stress on the components involved in guiding the eccentric wheel is reduced sharply. Furthermore, especially quiet operation of the eccentric gear wheel transmission is achieved, and the transmission can withstand substantially heavier loads, and mechanical wear is far less in comparison to conventional gears.
By means of the characteristics recited in the dependent claims, advantageous refinements of the eccentric gear wheel transmission defined by the main claim are possible.
If instead of the one guide pinion, a plurality of guide pinions disposed symmetrically about the eccentric wheel are used, then the active forces and thus the mechanical stress are distributed uniformly. It is for instance conceivable for two to three guide pinions to be disposed around the eccentric wheel, offset by 180xc2x0 or 120xc2x0 from one another as applicable.
The advantageous guidance of the eccentric wheel is attained by means of a guide pinion eccentric element, disposed on the guide pinion, that engages an oblong slot of the eccentric wheel. The eccentric element of the guide pinion can move back and forth in this oblong slot of the eccentric wheel and can thus receive one of two linear motion components of the circular motion of the eccentric wheel.
If the guide pinion has a set of external teeth that meshes with a set of external teeth of the rotational drive mechanism, then the motion of the eccentric wheel and the guide pinion are automatically synchronized which is a further advantage.
One condition for the guidance according to the invention of the eccentric wheel is that the eccentricity of the eccentric element of the guide pinion correspond to the eccentricity of the eccentric element that is connected to the eccentric wheel. This creates a precondition for preventing torsion of the eccentric wheel.
The disposition of the guide pinion relative to the eccentric wheel should also be done such that the center point of the eccentric element and the center point of the eccentric element of the guide pinion, regardless of the position of the rotational drive mechanism, are located on a line that extends parallel to a line through the shaft of the rotational drive mechanism and to a pin connected to the guide pinion. This meets a further condition so that the eccentric wheel is secured against torsion yet can be kept unhindered in terms of its eccentric motion. Thus the force transmission from an electric motor to a power takeoff pinion is also assured.
It is especially advantageous if the guide pinion is rotatably connected to a pin that protrudes into a transmission housing part and is solidly connected to it. This pin can be integrally formed onto the transmission housing part, and the guide pinion is simply mounted on this pin during assembly.